Satellite relay station using antenna diversity selection



June 25, 1963 R. SILBERSTEIN 3,095,538

SATELLITE RELAY STATION USING ANTENNA DIVERSITY SELECTION Filed on. 28. 1960 a Sheets-Sheet 1 TRANSMITTER REM v59 RE 65/ vE/e 5 TRANSMITTER {/4 4 Z \P D/VEPS/ TV SELECTOR FOR 0/ VEPS/TY SELECTOR FOR TRANSMITT/NG AND ATE/V/NG TRANSMITTING AND fiECE/V/NG ANTENNAS [F/GS- ZAND J) ANTENNAS (FIGS. 2 AND 3) TERMINAL TERMINAL STA T/ON 5T4 T/ON IN VENTOR Flt/2am Salbenszezh BY fizz W W M ATTORNEYS TRANSMITTING ANTENNAS June 25, 1963 R. SILBERSTEIN SATELLITE RELAY STATION USING ANTENNA DIVERSITY SELECTION Filed 001;. 28, 1960 3 Sheets-Sheet 3 W m ATTORNEYS Patented June 25, 1963 3,995,533 SATELLITE RELAY STATlUN USING ANTEIINA DIVERSHTY SELECTIQN Richard Silberstein, Boulder, Colo., assignor to the United States of America as represented by the Secretary of Commerce Filed Oct. 23, 196i), Ser. No. 65,876 8 Claims. (Cl. 325-4) This invention relates to a radiant energy relay station and in particular to one using receiving and transmitting antenna diversity selection.

' it is well known that the path of transmission followed by a microwave or VHF signal is limited in range along the line of sight, that any object in the path adversely affects the ability of a station to receive transmitted signals. To extend the range of transmission it has been proposed in the prior art to have relay stations carried in airplanes or satellites flying at considerable heights or circling the earth. These systems generally employ a directive receiving and transmitting antenna at each relay station with precise sensing devices and accurate moving parts to maintain each antenna pointed toward an adjacent station in the system. in addition to requiring the maintenance of delicate components, which is a distinct disadvantage, when the station is located in a satellite, the antenna positioning operation uses fuel or energy that may be limited in supply.

Accordingly, it is an object of the present invention to provide a relay station wherein the direction of transmission and reception of signals may be controlled with a minimum of power.

Another object is to provide a relay station utilizing diversity antenna selection techniques enabling the receiving and transmitting antennas to be lined in space.

Another object is to provide a terminal station with a diversity selector so that signals transmitted from a remote station effect the selection in the former of the most suited antennas for receiving signals from and transmitting signals to the latter.

With these and other objects in view, reference is now made to the following description taken in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures and wherein:

FIG. 1 is a block diagram of an embodiment of the invention; and

FIGS. 2 and 3 are detailed circuit diagrams of the diversity selector for the transmitting and receiving antennas shown in block form in FIG. 1.

In applying the teachings of the present invention, a communication system may be provided wherein signals sent from a terminal station are retransmitted by a relay station to another terminal station while signals from the latter are retransmitted to the former. The relay station may be placed in a desired geographical location, e.g., a satellite circling the earth. The signals that are transmitted from each terminal station, when received and applied to a diversity selector in the relay station, effect the selection of both a receiving and transmitting antenna. The antennas are used in receiving signals from and retransmitting signals to the terminal station.

The principles of the present invention may be employed in a system for communication between a pair of stations so that the signals received in each station efiect the selection in the receiving station of the most suited antenna for receiving signals from and transmitting sig nals to the other station.

The teachings of the present invention may also be used to provide a station with an arrangement for selecting the best antenna of a plurality of antennas in receiving signals from a distant station. In such an arrangement,

the signals received on a plurality of antennas are sequentially applied to a plurality of selecting circuits, each associated with a respective one of the receiving antennas. The selecting circuits are so interconnected that only one is activated in dependency upon the magnitude of the signals applied thereto. When activated, the selecting circuit couples the receiving antenna associated therewith, which is the most suited antenna for receiving the si 'nals, to a receiver.

Referring to FIG. 1, parabolas 9, 10 and 11, positioned on the surface of satellite 12, contain receiving elements or antennas A to F and transmitting elements or antennas A to F'." Receiving antennas 'A to C and transmitting antennas A to C are connected to diversity selector 13 while receiving antennas D to F and transmitting antennas D to F are connected to diversity selector 14. The selectors are shown in detail in H68. 2 and 3. The output of selector 13 is applied through receiver 15 and transmitter 16 to selector 14, and the output of selector 14 is applied to selector 13 through receiver 17 and transmitter 18. Although only three parabolas 9-11 are shown, by way of example, it is understood that satellite .12 may be provided with as many parabolas each containing as many antennas or driven elements as desired. In another embodiment, the satellite may contain a plurality of parabolic antennas or instead of receiving and transmitting antennas A to F and A to F, a single set of antennas and transmit-receive switching.

In operation, signals on frequency 1, are transmitted from terminal station 26 and relayed on frequency by the relay station on satellite 12 to terminal station 21, while simultaneously signals on f are transmitted from station 21 and relayed to station 20 on frequency f Frequency f controls diversity selector 13 in such a manner that the most suitable receiving antenna A to C is used to receive signals from terminal station 29 and the most suitable transmitting antenna A to C is used to send signals on frequency 5, to the latter station. Likewise, selector 14 is controlled by frequency f to select the best receiving and transmitting antenna D to F and D to F, respectively, for communication between terminal stations 21 and the relay station on satellite 12. It is understood that the signals transmitted on frequencies f and 3 may be a wide variety of intelligence and/or synchronizing signals.

The diversity selecting techniques employed may best be understood by referring to FIGS. 2 and 3. Everything shown in these figures, except receiver 15, transmitter 18 and receiving and transmitting antennas A to C and A to C, respectively, are contained in diversity selector 13 shown in FIG. 1. Diversity selector 14 is identical to selector 13 with the exception that the former is connected to transmitter 16, receiver 17, receiving and transmitting antennas D to F and D to F, respectively.

In FIG. 2, receiving antenna A, connected to the primary of transformer 26, is coupled through one secondary to diodes 27, 28 and through the other secondary to diodes 29, 30. Likewise, receiving antenna B is coupled through transformer 31 to diodes 32 to 35, and antenna C through transformer 36 to diodes 37 to 40. Diodes 27, 32, and 37 are connected to one side of the primary of transformer 43, While diodes 28, 33 and 38 are connected to the other side, all the diodes having the same polarity. The secondary of transformer 43 is positioned between the input of sampling receiver 44 and ground. The center tap on the primary is grounded. Diodes 29, 34 and 39 are connected to one side of the primary of transformer 45, while diodes 30, 35 and 40 are connected to the other side of the primary, all the diodes again having the same polarity. The secondary of transformer 45 is placed between ground and the input of communication receiver 15. Current limiting resistor 4-6 couples the center tap on the primary of transformer to source of positive potential 47. Variable capacitor 4-8 is located between the anode of diode 27 and the cathode of diode 28 and variable capacitor 49' between the anode of diode 28 and the cathode of diode 27. Likewise, variable capacitors 50 to 59 are connected between the anode and cathode of their associated diodes. Thus, the variable capacitors may be set to neutralize the internal capacities of their associated diodes. The output of sampling receiver 44 is applied in parallel to gates 60 to 63; the output of counting ring 65 in parallel to the center taps on transformers 26, 31 and 36 and in parallel to gates 69 to 63.

The output of gate Gil appearing on terminal 79 in FIG. 2 is applied to the control grid of electron tube 71 in FIG. 3 through terminal 72, transformer 73, diodeg74, and RC circuit 75 comprising resistor 77 in parallel with capacitor 77. Variable capacitor 78 is located across the primary of transformer 73, and variable capacitor 79 across the secondary. The output of gate 61 is fed through terminals 82, 83, transformer 84, diode 85, and RC circuit 86 comprising resistor 87 in parallel with capacitor 88 to the control grid of electron tube 89. Variable capacitor 90 is connected across the primary of transformer 84- and variable capacitor 91 across the secondary. In a similar manner, the output of gate 63 is fed through terminals 93, 94, transformer 95, diode 96, and RC circuit 97, comprising resistor 98 in parallel with capacitor 99, to the control grid of electron tube 100. Variable capacitor 191 is positioned across the primary of transformer 95, while variable capacitor 1112 is positioned across the secondary. One side of RC circuits 75, 86 and 97, each selected to have a long-time constant, are connected to the control grids of electron tubes 71, 89 and 100, respectively. The other side of each RC circuit is connected through resistors 103, 104, and 105, respectively, to the negative side of DC. power source 110. Power source 106 is applied to the plates of electron tubes 71, 89 and 1% through resistors 114- to 116, respectively. The cathode of each electron tube is connected to ground.

The plate of electron tube 71 is coupled to the control grid of electron tube 1% through resistor 121, and to the control grid of electron tube 89 through resistor 124, while the plate of electron tube 89 is coupled to the control grid of electron tube 71 hrough resisor 122 and to the control grid of electron tube 190 through resistor 123. Finally, the plate of electron tube 1% is tied to the control grid of electron tube 71 through resistor 125 and to the control grid of electron tube 89' through resistor 126.

The plate of electron tube 71 in FIG. 3 is connected to a center tap on a secondary of transformer st in FIG. 2 through terminals 130, 131. In the same manner the plate of electron tube 89 is connected to a center tap on one secondary in transformer 31 through terminals 132, 133 and the plate of electron tube 101 to a center tap on one secondary of transformer 36 through terminals 134-, 135. The plates of electron tubes 71, 89 and 100 are tied to ground through a respective one of the relays 141 141, 142. Each relay has a high resistance and when deenergized connects one of the transmitting antennas A, B, or C to transmitter 18 which receives its input from receiver 17 in FIG. 1.

It is understood that, instead of relays to 142, transmitting antennas A to C may each be provided with an amplifier stage including an electron tube that is biased to conduction when the associated antenna is selected for operation by diversity selector 13.

In operation, as terminal station 20 transmits a signal on frequency h which is received on antennas A to C, counting ring 65 applies control voltages to diodes 27, 28, 32, 33, 37 and 38. The control voltages are polarized in such a manner that the antenna circuits associated with the diodes are sequentially rendered conductive, thereby applying the signal received on antennas A to C in sequence to sampling receiver 44. Variable capacitors 48 to 53 neutralize the internal capacitances of the diodes just referred to, preventing the signal on the antennas from being applied to sampling receiver 44 when the diodes are blocked.

The output of sampling receiver 44 is fed in parallel to gates 69 to 63, which are sequentially opened by signals applied from counting ring 65, to feed the rectified output of the receiver in sequence through RC circuits 75, 86 and 97, which have discharge time constants much longer than the period of one sampling sequence. Thus, the control grids of electron tubes 71, 89 and 1139 have D.C. voltages upon them proportional to the outputs of antennas A, B and C. Because of the mutual coupling of the electron tubes through resistors 121 to 125 which have appropriate values, the electron tube having the highest positive control grid potential applied thereto will conduct while the others are blocked. If, for example, because antenna A has the strongest output the voltage developed across RC circuit 75 has a higher value than the voltage across RC circuits 86 and 97, electron tube 71 will conduct and the mutual coupling provided through resistors 124 and 121 will block electron tubes 89 and 190.

When electron tubes 71, 89 and 101 are non-conducting, the current flow through relays 141 to 142 is sulficient to energize the relays, placing their armatures in the position shown in FIG. 3 for relays 141, 142. In this operating condition, power source in FIG. 3 will back bias diodes 29, 30, 34-, 35, 39 and 419 in FIG. 2

- so that receiving antennas A to C are decoupled from receiver 15.

When electron tube 71 conducts, current flowing through resistor 114 results in a voltage drop having a magnitude such that insufficient current flows through the circuit to energize relay 1 10. The armature of the relay will therefore move to the position shown in FIG. 3, connecting antenna A to transmitter 13. Signals received from station 21 through receiver 17 then control transmitter 18, which retransmits the signals through antenna A to station 20. Simultaneously, the voltage drop across resistor 114 lowers the bias applied by power source 196 to the cathodes of diodes 29 and 30. The relation between the bias applied by power sources 47 and 106 to the diodes, when a voltage is developed across resistor 114, is such that the diodes are forward biased and receiving antenna A is coupled to receiver 15. The output of receiver 15 is then applied to transmitter 16 and sent to station 21 by way of one of the transmitting antennas D to F. The transmitting antenna employed for this purpose is selected and activated by diversity selector 14 in dependency upon a signal received from station 21.

When electron tubes 89 and 1190 conduct, the operation is similar to that indicated in connection with electron tube 7 1 and need not be considered further.

Thus, it is seen that signals transmitted on frequency h from terminal station 26 control antenna diversity elector 13 to elfect the selection of the antenna receiving the strongest signals from that station and the best transmitting antenna for sending signals to that station. At the same time, signals transmitted from terminal station 21 on frequency A control diversity selector 14 to select the best receiving and transmitting antennas for transmitting signals to and receiving signals from that terminal station.

Various modifications'are contemplated and obviously may be resorted to by those skilled in the art without departing from the spirit and scope of the present invention as hereinafter defined by the appended claims.

What is claimed is:

l. A diversity antenna selection system comprising: a plurality of receiving antennas, a sampling receiver, means for sequentially applying the output of each of said receiving antennas to said sampling receiver, a plurality of selecting circuits interconnected so that only one selecting circuit is activated in dependency upon the relative magnitudes of the signals applied to said selecting circuits, each selecting circuit being associated With a respective one of said receiving antennas, means for applying the output of said sampling receiver in sequence to each of said selecting circuits, a second receiver, and means responsive to the output of each of said selecting circuits when activated for coupling the receiving antenna associated with the selecting circuit to said second receiver.

2. A diversity antenna selection system comprising: a plurality of receiving antennas, a plurality of transmitting antennas, a plurality of selecting circuits interconnected so that only one selecting circuit is activated in dependency upon the relative magnitudes of the signals applied to said selecting circuits, each selecting circuit being associated with a respective one of said receiving antennas and a respective one of said transmitting antennas, means for sequentially coupling the output of each of said receiving antennas to said selecting circuits, a transmitter, and means responsive to the output of each of said selecting circuits when activated for coupling the transmitting antenna associated with the selecting circuit to said transmitter.

3. A diversity antenna selection system comprising: a plurality of receiving antennas, a sampling receiver, means for sequentially applying the output of each of said receiving antennas to said sampling receiver, a plurality of transmitting antennas, a plurality of selecting circuits interconnected so that only one selecting circuit is activated in dependency upon the relative magnitudes of the signals applied to said selecting circuits, each selecting circuit being associated with a respective one of said transmitting antennas, means for applying the output of said sampling receiver in sequence to each of said selecting circuits, a transmitter, and means responsive to the output of each of said selecting circuits when activated for coupling the transmitting antenna associated with the selecting circuit to said transmitter.

4. A diversity antenna selection system comprising: a plurality of receiving antennas, a sampling receiver, means for sequentially applying the output of each of said receiving antennas to said sampling receiver, a plurality of transmitting antennas, a plurality of selecting circuits interconnected so that only one selecting circuit is activated in dependency upon the relative magnitudes of the signals applied to said selecting circuits, each selecting circuit being associated with a respective one of said receiving antennas and a respective one of said transmitting antennas, means for applying the output of said sampling receiver in sequence to each of said selecting circuits, a transmitter, a second receiver, means responsive to the output of each of said selecting circuits when activated for coupling the receiving and transmitting antenna associated with the selecting circuit to said second receiver and said transmitter, respectively.

5. A radiant energy relay station comprising: a plurality of first and second receiving antennas, a plurality of first and second transmitting antennas, a first and second diversity antenna selector, means for coupling said first receiving and said first transmitting antennas to said first deversity antenna selector, means for coupling said second receiving and said second transmitting antennas to said second diversity antenna selector, a first receiver connected to said first diversity selector, a first transmit- 6 ter connected between said first receiver and said second diversity selector, 2. second receiver connected to said second diversity antenna selector, and a second transmitter connected between said second receiver and said first diversity antenna selector.

6. The radiant energy relay system recited in claim 5 wherein the first and second antenna diversity selector each comprises: a plurality of selecting circuits interconnected so that only one selecting circuit is activated in dependency upon the relative magnitudes of the signals applied to said selecting circuits, each selecting circuit being associated with a respective one of the receiving antennas and a respective one of the transmitting antennas coupled to the diversity antenna selector, means for applying the output of each of the receiving antennas to the selecting circuits, and means responsive to the output of each of said selecting circuits when activated for coupling the receiving and transmitting antenna associated with the selecting circuit to the receiver and transmitter, respectively, connected to the diversity antenna selector.

7. The radiant energy relay system recited in claim 5 wherein the first and second antenna diversity selector each comprises: a plurality of selecting circuits interconnected so that only one selecting circuit is activated in dependency upon the relative magnitudes of the signals applied to said selecting circuits, each selecting circuit being associated with a respective one of the receiving antennas and a respective one of the transmitting antennas coupled to the diversity antenna selector, means for coupling the output of each of the receiving antennas in sequence to its associated selecting circuit, and means responsive to the output of each of said selecting circuits when activated for coupling the receiving and transmitting antenna associated with the selecting circuit to the receiver and transmitter, respectively, connected to the diversity antenna selector.

8. The radiant energy relay system recited in claim 5 wherein the first and second antenna diversity selector each comprises: a sampling receiver, means for sequentially applying the output of each of the receiving antennas coupled to the antenna diversity selector to said sampling receiver, a plurality of selecting circuits interconnected so that only one selecting circuit is activated in dependency upon the relative magnitudes of the signals applied to said selecting circuits, each selecting circuit being associated with a respective one of the receiving antennas and a respective one of the transmitting antennas coupled to the diversity antenna selector, means for applying the output of said sampling receiver in sequence to each of said selecting circuits, and means responsive to the output of each of said selecting circuits when activated for coupling the receiving and transmitting antenna associated with the selecting circuit to the receiver and transmitter, respectively, connected to the diversity antenna selector.

References Cited in the file of this patent UNITED STATES PATENTS 2,004,127 Peterson June 11, 1935 2,037,865 Potter Apr. 21, 1936 2,059,081 Beers Oct. 27, 1936 2,290,992 Peterson July 28, 1942 2,521,696 De Armond Sept. 12, 1950 2,892,930 Magn-uski et al. June 30, 1959 2,904,677 Heidester Sept. 15, 1959 2,937,268 Downie et al May 17, 1960 2,985,755 Giesselman May 23, 1961 

1. A DIVERSITY ANTENNA SELECTION SYSTEM COMPRISING: A PLURALITY OF RECEIVING ANTENNAS, A SAMPLING RECEIVER, MEANS FOR SEQUENTIALLY APPLYING THE OUTPUT OF EACH OF SAID RECEIVING ANTENNAS TO SAID SAMPLING RECEIVER, A PLURALITY OF SELECTING CIRCUITS INTERCONNECTED SO THAT ONLY ONE SELECTING CIRCUIT IS ACTIVATED IN DEPENDENCY UPON THE RELATIVE MAGNITUDES OF THE SIGNALS APPLIED TO SAID SELECTING CIRCUITS, EACH SELECTING CIRCUIT BEING ASSOCIATED WITH A RESPECTIVE ONE OF SAID RECEIVING ANTENNAS, MEANS FOR APPLYING THE OUTPUT OF SAID SAMPLING RECEIVER IN SEQUENCE TO EACH OF SAID SELECTING CIRCUITS, A SECOND RECEIVER, AND MEANS RESPONSIVE TO THE OUTPUT OF EACH OF SAID SELECTING CIRCUITS WHEN ACTIVATED FOR COUPLING THE RECEIVING ANTENNA ASSOCIATED WITH THE SELECTING CIRCUIT TO SAID SECOND RECEIVER. 